Hi,
I think there are important differences between "frbr:item" and
"holdings". (There may be interpretations of "holdings" other than
what I'll use here, which is why it's probably useful to clarify the
term.)
In a local catalog, there might be one bibliographic record that has
two holdings records (e.g. one for the main library, one for the
engineering library), and then each of those might have multiple item
records representing multiple copies (e.g. 3 copies at main, 2 at
engineering). I would consider each item record (not each holdings
record) to correspond to a frbr:item.
In WorldCat, a bibliographic record may list multiple libraries as
"holding" institutions, even though each of those may have multiple
copies. From what I understand, WorldCat Local doesn't track
individual copies, but has to query your local catalog to get the copy
info (location, call number, availability).
In theory, each copy of a particular publication is an frbr:item of
the frbr:manifestation. But we have traditionally grouped these
copies together by location (by institution and within an
institution). That is, our current systems don't really have:
manifestation --> item
but something more like:
manifestation --> [ institution --> ] location --> item
At some point, in a future frbrized universal catalog, we may decide
it's better to drop that tradition and just have each item linked
directly to the manifestation. (The item itself would contain the
info about the owning institution, location, etc.)
Keith
> > ... anyway, the point is -- you have to define 'holding', or you can't be
> > assured that the response to your request is the correct granularity of
> > information to answer the question you're trying to ask.
>
> Ok, then I'd define a holding an instance of frbr:item with the
> properties "location" (a building, an institution, an URL...),
> "identifier" (call-number, item-number, URL...) and "availability"
> (available, next week, only on campus, free for download...). As shown
> in my ad-hoc example "location" can be nested, but that's not the point.
> Defining holding is not the problem - you just have to look how
> holdings are *practically* used in libraries (instead of starting a
> theoretical discussion). The problem is more how to get the data out of
> library systems.
